In automobiles, the rotation of an engine is a source of driving force for various auxiliary machines such as a supercharger, an air compressor used for an air-conditioner or a power steering pump. Conventionally, a means for transmitting the rotation torque of an engine to the auxiliary machines has been only a combination of fixed pulleys provided on a crank shaft and the input shaft of an auxiliary machine and a V-belt between both fixed pulleys. This means produces no change of a diameter of a pitch circle formed between both pulleys. As an engine speed increases, that of the auxiliary machine also increases in proportion. For example, though the auxiliary machine requires just 2000 to 3000 r.p.m., the machine has been rotated more than required. It has resulted in bringing about the problems of heating and in addition large drive loss of the engine.
To cope with these problems, it is favorable to set the number of revolutions of the auxiliary machine to be high when the engine rotates at low speed in order to suppress increasing of the number of revolutions of the auxiliary machine though the number of revolutions of the engine increases. This method enables the engine to rotate at high speed as well as to make the engine smaller since the driving force is saved with the number of revolutions.
In the prior art, a mechanical stepless speed variator employing the V belt has been used for various industrial fields. The construction is that a drive shaft and a driven shaft are provided with fixed conical sieves respectively and the driven shaft is provided with a sliding sieve accessible with respect to the fixed sieve. The sliding sieve is designed to be pushed in the thrust direction by a coil spring. The fixed sieve has a feed screw and the sliding sieve has a female screw, and during rotation of the pulley, a handle connected to the feed screw is rotated to push the sliding sieve in the thrust direction so as to adjust the interval between both sieves for changing the speed. This construction needs external operations and therefore cannot be used for the auxiliary machine driving system in automobiles.
Furthermore, the Japanese Patent Laid-open No. 26845/1985 discloses the system for controlling the position of a movable cone sieve composing one side of a pulley by using an oil pressure servo mechanism.
This antecedent has the following construction; a movable cone pulley has a fixed cylinder in the axis, the piston rod of the fixed cylinder is pressed to the end of the movable cone pulley, the piston rod includes a duct formed thereon, the rear end of which passes through a cylinder chamber and the front end of which opens toward the end of the piston rod, and the duct is opened or shut by a sleeve through a flyweight of a drive shaft, a spring, an arm or a rod.
This construction has the shaft of the movable cone pulley located in series with the external piston rod so that the force of changing a pulley ratio by the change of driven side load is opposed to the oil pressure immediately applied to the piston rod. With the change of the driven side load, therefore, the pulley ratio is changed to make the drive side load constant (the pulley ratio is changed as the driven side load changes). It results in bringing about the problem that this prior art cannot be applied to drive control for an auxiliary machine of an automobile which needs a constant pulley ratio even in case of load change though it can be applied to the speed variator of a bicycle provided with a prime mover.
Moreover, this speed variator has the flyweight located at the rear of the fixed pulley and the piston located at the rear of the movable pulley, connects the slider for controlling ejection of oil from the duct formed on the piston to the arm connecting both pulleys, and employs an external large exclusive fixed cylinder and pump. Hence, this prior art is made bulky in the axial dimensions and unfeasible to be installed into an automobile.